Wireless Circuitry with Self-Calibrated Harmonic Rejection Mixers

ABSTRACT

An electronic device may include a harmonic rejection mixer with a delay line, mixer array, and load. The delay line may generate LO phases. Each mixer in the array may have a first input that receives an LO phase and a second input coupled to an input switch and the first input of the next mixer circuit through an inter-mixer switch. The load may include a set of switches. In a transmit mode, the input switches and set of switches may be closed while the inter-mixer switches are open. In a self-calibration mode, the input switches and set of switches may be open while the inter-mixer switches are closed. A controller may sweep through phase codes for the programmable delay line while storing a digital output from the load. The controller may calibrate the phase code based on the digital output.

This application is a continuation of U.S. patent application Ser. No.17/031,753, filed Sep. 24, 2020, which is hereby incorporated byreference herein in its entirety.

FIELD

This disclosure relates generally to electronic devices and, moreparticularly, to electronic devices with wireless communicationscircuitry.

BACKGROUND

Electronic devices are often provided with wireless communicationscapabilities. An electronic device with wireless communicationscapabilities has wireless communications circuitry that includes one ormore antennas. Wireless transmitter circuitry in the wirelesscommunications circuitry generates radio-frequency signals using a localoscillator. The antennas transmit the radio-frequency signals.

It can be challenging to form satisfactory wireless transmittercircuitry for an electronic device. If care is not taken in the wirelesstransmitter circuitry design, harmonics of the local oscillator canundesirably degrade the radio-frequency signals transmitted by theantennas.

SUMMARY

An electronic device may include wireless circuitry for performingwireless Communications. The wireless circuitry may include a basebandprocessor, a transmitter, and an antenna. The transmitter may include alocal oscillator generator and a harmonic rejection mixer. The localoscillator generator may generate local oscillator (LO) waveforms. Theharmonic rejection mixer may include a programmable delay line, a mixerarray, an adjustable load, and a controller. The programmable delay linemay generate a set of LO phases based on the LO waveforms. The harmonicrejection mixer may be operable in a transmit mode and in a calibrationmode.

The mixer array may include a set of mixer circuits. Each mixer circuitmay have a first input and a second input. The first input may receive arespective one of the LO phases. The second input may be coupled to aninput path through an input switch. The second input may also be coupledto the first input of the next mixer circuit in the mixer array throughan inter-mixer switch. The adjustable load may include a set ofswitches. In the transmit mode, the input switches in the mixer arraymay be closed, the inter-mixer switches in the mixer array may be open,and the set of switches in the adjustable load may be closed. The mixerarray may generate radio-frequency signals on an output path based oninput signals on the input path and the set of LO phases generated bythe programmable delay line. The adjustable load may amplify theradio-frequency signals for transmission by an antenna.

In the calibration mode, the input switches in the mixer array may beopen, the inter-mixer switches in the mixer array may be closed, and theset of switches in the adjustable load may be open. The mixer array mayact as a phase detector and generate a direct current (DC) voltage onthe output path based on the LO phases generated by the programmabledelay line. The programable load may output the DC voltage. Ananalog-to-digital converter may generate a digital output based on theamplified DC voltage. The controller may store the digital output. Thecontroller may sweep through different phase codes provided to theprogrammable delay line while gathering and storing the digital output.The controller may process the stored digital output to identify a zerocrossing point of the DC voltage. The controller may identify acalibrated phase code associated with the zero crossing point and mayprovide the calibrated phase code to the programmable delay line. Theprogrammable delay line may generate calibrated LO phases for the mixerarray for use during subsequent radio-frequency signal transmission.This may allow the harmonic rejection mixer to cancel out harmonicinterference from harmonic modes of the LO even as operating conditionsfor the device change over time.

An aspect of the disclosure provides an electronic device. Theelectronic device can have a mixer array. The mixer array can upconvertinput signals on an input path to produce radio-frequency signals on anoutput path. The mixer array can have a first mixer circuit. The firstmixer circuit can have a first input that receives a first localoscillator (LO) phase, a second input that receives the input signals,and a first output coupled to the output path. The mixer array can havea second mixer circuit. The second mixer circuit can have a third inputthat receives a second LO phase that is phase-delayed with respect tothe first LO phase, a fourth input that receives the input signals, anda second output coupled to the output path. The mixer array can have aninter-mixer switch coupled between the second input of the first mixercircuit and the third input of the second mixer circuit.

An aspect of the disclosure provides a method for operating mixercircuitry. The method can include, with a programmable delay line,generating a first local oscillator (LO) phase, a second LO phase, and athird LO phase. The second LO phase can be phase-delayed with respect tothe first LO phase. The third LO phase can be phase-delayed with respectto the second LO phase. The method can include, with a first mixercircuit in a mixer array, mixing the first LO phase with the second LOphase. The method can include, with a second mixer circuit in the mixerarray, mixing the second LO phase with the third LO phase. The methodcan include, with the mixer array, outputting a direct current (DC)voltage onto an output path. The DC voltage can be produced by at leastthe first and second mixer circuits. The method can include, with anadjustable load coupled to the output path, amplifying the DC voltage togenerate an amplified DC voltage. The method can include, with ananalog-to-digital converter (ADC) coupled to the output path, generatinga digital output based on the amplified DC voltage. The method caninclude, with a controller coupled to the ADC, adjusting the first,second, and third LO phases based on the digital output.

An aspect of the disclosure provides an electronic device. Theelectronic device can have an input path that receives input signals.The electronic device can have first and second output lines. Theelectronic device can have a programmable delay line that generates aset of local oscillator (LO) phases. The electronic device can have amixer array coupled between the input path and the first and secondoutput lines. The mixer array can generate radio-frequency signals onthe first and second output lines based on the input signals and the setof LO phases. The electronic device can have an adjustable load coupledto the first and second output lines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an illustrative electronic devicehaving a wireless transmitter with a harmonic rejection mixer inaccordance with some embodiments.

FIG. 2 is a circuit diagram of an illustrative harmonic rejection mixerin accordance with some embodiments.

FIG. 3 is a state diagram showing how an illustrative harmonic rejectionmixer may be operable in a transmit mode and in a calibration mode inaccordance with some embodiments.

FIG. 4 is a circuit diagram showing the harmonic rejection mixer of FIG.2 operated in the transmit mode in accordance with some embodiments.

FIG. 5 is a circuit diagram showing the harmonic rejection mixer of FIG.2 operated in the calibration mode in accordance with some embodiments.

FIG. 6 is a circuit diagram of an illustrative mixer circuit that may beused in a harmonic rejection mixer in accordance with some embodiments.

FIG. 7 is a flow chart of illustrative steps involved in calibrating thephase code for a harmonic rejection mixer in accordance with someembodiments.

FIG. 8 is a plot illustrating how a zero-crossing point may beidentified while calibrating the phase code for a harmonic rejectionmixer in accordance with some embodiments.

DETAILED DESCRIPTION

Electronic device 10 of FIG. 1 may be a computing device such as alaptop computer, a desktop computer, a computer monitor containing anembedded computer, a tablet computer, a cellular telephone, a mediaplayer, or other handheld or portable electronic device, a smallerdevice such as a wristwatch device, a pendant device, a headphone orearpiece device, a device embedded in eyeglasses or other equipment wornon a user's head, or other wearable or miniature device, a television, acomputer display that does not contain an embedded computer, a gamingdevice, a navigation device, an embedded system such as a system inwhich electronic equipment with a display is mounted in a kiosk orautomobile, a wireless internet-connected voice-controlled speaker, ahome entertainment device, a remote control device, a gaming controller,a peripheral user input device, a wireless base station or access point,equipment that implements the functionality of two or more of thesedevices, or other electronic equipment.

As shown in the schematic diagram FIG. 1, device 10 may includecomponents located on or within an electronic device housing such ashousing 12. Housing 12, which may sometimes be referred to as a case,may be formed of plastic, glass, ceramics, fiber composites, metal(e.g., stainless steel, aluminum, metal alloys, etc.), other suitablematerials, or a combination of these materials. In some situations,parts or all of housing 12 may be formed from dielectric or otherlow-conductivity material (e.g., glass, ceramic, plastic, sapphire,etc.). In other situations, housing 12 or at least some of thestructures that make up housing 12 may be formed from metal elements.

Device 10 may include control circuitry 14. Control circuitry 14 mayinclude storage such as storage circuitry 16. Storage circuitry 16 mayinclude hard disk drive storage, nonvolatile memory (e.g., flash memoryor other electrically-programmable-read-only memory configured to form asolid-state drive), volatile memory (e.g., static or dynamicrandom-access-memory), etc. Storage circuitry 16 may include storagethat is integrated within device 10 and/or removable storage media.

Control circuitry 14 may include processing circuitry such as processingcircuitry 18. Processing circuitry 18 may be used to control theoperation of device 10. Processing circuitry 18 may include on one ormore microprocessors, microcontrollers, digital signal processors, hostprocessors, baseband processor integrated circuits, application specificintegrated circuits, central processing units (CPUs), etc. Controlcircuitry 14 may be configured to perform operations in device 10 usinghardware (e.g., dedicated hardware or circuitry), firmware, and/orsoftware. Software code for performing operations in device 10 may bestored on storage circuitry 16 (e.g., storage circuitry 16 may includenon-transitory (tangible) computer readable storage media that storesthe software code). The software code may sometimes be referred to asprogram instructions, software, data, instructions, or code. Softwarecode stored on storage circuitry 16 may be executed by processingcircuitry 18.

Control circuitry 14 may be used to run software on device 10 such assatellite navigation applications, internet browsing applications,voice-over-internet-protocol (VOIP) telephone call applications, emailapplications, media playback applications, operating system functions,etc. To support interactions with external equipment, control circuitry14 may be used in implementing communications protocols. Communicationsprotocols that may be implemented using control circuitry 14 includeinternet protocols, wireless local area network (WLAN) protocols (e.g.,IEEE 802.11 protocols—sometimes referred to as Wi-Fi®), protocols forother short-range wireless communications links such as the Bluetooth®protocol or other wireless personal area network (WPAN) protocols, IEEE802.11ad protocols (e.g., ultra-wideband protocols), cellular telephoneprotocols (e.g., 3G protocols, 4G (LTE) protocols, 5G protocols, etc.),antenna diversity protocols, satellite navigation system protocols(e.g., global positioning system (GPS) protocols, global navigationsatellite system (GLONASS) protocols, etc.), antenna-based spatialranging protocols (e.g., radio detection and ranging (RADAR) protocolsor other desired range detection protocols for signals conveyed atmillimeter and centimeter wave frequencies), or any other desiredcommunications protocols. Each communications protocol may be associatedwith a corresponding radio access technology (RAT) that specifies thephysical connection methodology used in implementing the protocol.

Device 10 may include input-output circuitry 20. Input-output circuitry20 may include input-output devices 22. Input-output devices 22 may beused to allow data to be supplied to device 10 and to allow data to beprovided from device 10 to external devices. Input-output devices 22 mayinclude user interface devices, data port devices, and otherinput-output components. For example, input-output devices 22 mayinclude touch sensors, displays, light-emitting components such asdisplays without touch sensor capabilities, buttons (mechanical,capacitive, optical, etc.), scrolling wheels, touch pads, key pads,keyboards, microphones, cameras, buttons, speakers, status indicators,audio jacks and other audio port components, digital data port devices,motion sensors (accelerometers, gyroscopes, and/or compasses that detectmotion), capacitance sensors, proximity sensors, magnetic sensors, forcesensors (e.g., force sensors coupled to a display to detect pressureapplied to the display), etc. In some configurations, keyboards,headphones, displays, pointing devices such as trackpads, mice, andjoysticks, and other input-output devices may be coupled to device 10using wired or wireless connections (e.g., some of input-output devices22 may be peripherals that are coupled to a main processing unit orother portion of device 10 via a wired or wireless link).

Input-output circuitry 20 may include wireless circuitry 24 to supportwireless communications. Wireless circuitry 24 (sometimes referred toherein as wireless communications circuitry 24) may include a basebandprocessor such as baseband processor 26, radio-frequency (RF)transmitter circuitry such as transmitter 28, and one or more antennas30. Baseband processor 26 may be coupled to transmitter 28 over basebandpath 32. Transmitter 28 may be coupled to antenna(s) 30 overradio-frequency transmission line path 52. If desired, radio-frequencyfront end circuitry may be interposed on radio-frequency transmissionline path 52.

In the example of FIG. 1, wireless circuitry 24 is illustrated asincluding only a single baseband processor 26 and a single transmitter28 for the sake of clarity. In general, wireless circuitry 24 mayinclude any desired number of baseband processors 26, any desired numberof transmitters 28, and any desired number of antennas 30. Each antennamay be coupled to transmitter 28 over a respective radio-frequencytransmission line path, for example. Transmitter 28 may transmitradio-frequency signals RF′ using antenna(s) 30. If desired, wirelesscircuitry 24 may also include one or more radio-frequency receivers forreceiving radio-frequency signals using antenna(s) 30 (e.g., theradio-frequency receiver and transmitter 28 may collectively form aradio-frequency transceiver for wireless circuitry 24).

Radio-frequency transmission line path 52 may be coupled to antennafeed(s) on antenna(s) 30. Each antenna feed may, for example, include apositive antenna feed terminal and a ground antenna feed terminal.Radio-frequency transmission line path 52 may have a positivetransmission line signal path such that is coupled to the positiveantenna feed terminal. Radio-frequency transmission line path 52 mayhave a ground transmission line signal path that is coupled to theground antenna feed terminal. This example is merely illustrative and,in general, antenna(s) 30 may be fed using any desired antenna feedingscheme. If desired, each antenna 30 may have multiple antenna feeds thatare coupled to one or more radio-frequency transmission line paths 52.

Radio-frequency transmission line path 52 may include transmission linesthat are used to route radio-frequency antenna signals within device 10.Transmission lines in device 10 may include coaxial cables, microstriptransmission lines, stripline transmission lines, edge-coupledmicrostrip transmission lines, edge-coupled stripline transmissionlines, transmission lines formed from combinations of transmission linesof these types, etc. Transmission lines in device 10 such astransmission lines in radio-frequency transmission line path 52 may beintegrated into rigid and/or flexible printed circuit boards.

Radio-frequency signals RF′ may be produced by transmitter 28 at acarrier frequency. The carrier frequency may lie within a correspondingfrequency band (sometimes referred to herein as a communications band orsimply as a “band”). The frequency bands handled by transmitter 28 mayinclude wireless local area network (WLAN) frequency bands (e.g., Wi-Fi®(IEEE 802.11) or other WLAN communications bands) such as a 2.4 GHz WLANband (e.g., from 2400 to 2480 MHz), a 5 GHz WLAN band (e.g., from 5180to 5825 MHz), a Wi-Fi® 6E band (e.g., from 5925-7125 MHz), and/or otherWi-Fi® bands (e.g., from 1875-5160 MHz), wireless personal area network(WPAN) frequency bands such as the 2.4 GHz Bluetooth® band or other WPANcommunications bands, cellular telephone frequency bands (e.g., bandsfrom about 600 MHz to about 5 GHz, 3G bands, 4G LTE bands, 5G New RadioFrequency Range 1 (FR1) bands below 10 GHz, 5G New Radio Frequency Range2 (FR2) bands between 20 and 60 GHz, etc.), near-field communicationsfrequency bands (e.g., at 13.56 MHz), satellite navigation frequencybands (e.g., a GPS band from 1565 to 1610 MHz, a Global NavigationSatellite System (GLONASS) band, a BeiDou Navigation Satellite System(BDS) band, etc.), ultra-wideband (UWB) frequency bands that operateunder the IEEE 802.15.4 protocol and/or other ultra-widebandcommunications protocols, and/or any other desired frequency bands ofinterest.

Antenna(s) 30 may be formed using any desired antenna structures. Forexample, antenna(s) 30 may include an antenna with a resonating elementthat is formed from loop antenna structures, patch antenna structures,inverted-F antenna structures, slot antenna structures, planarinverted-F antenna structures, helical antenna structures, monopoleantennas, dipoles, hybrids of these designs, etc. Filter circuitry,switching circuitry, impedance matching circuitry, and other circuitrymay be interposed within radio-frequency transmission line path 52, maybe incorporated into front end circuitry for antenna(s) 30, and/or maybe incorporated into antenna(s) 30 (e.g., to support antenna tuning, tosupport operation in desired frequency bands, etc.). These components,sometimes referred to herein as antenna tuning components, may beadjusted (e.g., using control circuitry 14) to adjust the frequencyresponse and wireless performance of antenna(s) 30 over time.

In radio-frequency transmitters, radio-frequency signals may beconstructed using local oscillator (LO) waveforms. For example, as shownin FIG. 1, transmitter 28 may include LO generator circuitry such as LOgenerator 40. LO generator 40 may produce local oscillator waveforms LOCon path 41 (sometimes referred to herein as local oscillator path 41 orLO path 41). In performing wireless transmission, baseband processor 26may provide baseband signals to transmitter 28 over baseband path 32.Transmitter 28 may include mixer circuitry that up-converts the basebandsignals to radio frequencies based on the local oscillator waveforms LOCoutput by LO generator 40.

Spectral purity is important for signal quality and integrity in themixer circuitry of transmitter 28. However, hard-switching mixers arerich with odd-order harmonics of the local oscillator. If care is nottaken, these odd-order harmonics can generate spurious signals or tonesthat cause error vector magnitude (EVM) degradation, blocker de-sense,and/or spurious emission mask violations in transmitter 28. For example,if the frequency of the local oscillator is close to the frequency ofthe signals input to the mixer circuitry for upconversion, the strongthird-order harmonic of the local oscillator would create an unwantedsignal at a frequency equal to three-times the frequency of the localoscillator minus the frequency of the signals input to the mixercircuitry for upconversion. This frequency is close to the desiredfrequency output by the mixer circuitry (e.g., the frequency of thelocal oscillator plus the frequency of the signals input to the mixercircuitry for upconversion). This unwanted signal would degrade the EVMof transmitter 28 if it overlaps with the in-band signal and wouldviolate the emission mask if it lies out-of-band. In arrangements wherea direct up-conversion mixer is used, the mixer would exhibit counterthird-order intermodulation (CIM3) issues.

The mixer circuitry in transmitter 28 may perform up-conversion usingthe fundamental mode of the local oscillator (e.g., as identified bywaveforms LOC) or, in another suitable arrangement, may performup-conversion using the third-order harmonic mode of the localoscillator. In these scenarios, a frequency tripler may be used in LOgenerator 40. The frequency tripler includes a voltage controlledoscillator (VCO) that generates a lower frequency local oscillator thatis tripled to a desired frequency (e.g., a frequency that is three-timesthe fundamental mode frequency of the lower frequency local oscillator).In this case, the third-order harmonic of the local oscillator (e.g., asidentified by waveforms LOC) may be used by the mixer circuitry ratherthan the fundamental mode of the local oscillator.

In order to mitigate EVM degradation and emission mask violation intransmitter 28 due to harmonics of the local oscillator, the mixercircuitry in transmitter 28 may include a harmonic rejection mixer suchas harmonic rejection mixer 38. In one suitable arrangement that isdescribed herein as an example, harmonic rejection mixer 38 mayup-convert intermediate frequency (IF) signals IFIN to radio-frequencysignals (e.g., radio-frequency signals RF′ for transmission byantenna(s) 30). This is merely illustrative and, if desired, harmonicrejection mixer 38 may up-convert baseband signals or signals at otherfrequencies to radio frequencies.

As shown in FIG. 1, transmitter 28 may include IF upconverter circuitrysuch as IF up-converter 34. IF upconverter 34 may upconvert the basebandsignals received over baseband path 32 into corresponding IF signalsIFIN. IF signals IFIN may be at frequencies between the frequency ofradio-frequency signals RF′ and the baseband frequency of the basebandsignals. IF upconverter 34 may provide IF signals IFIN to harmonicrejection mixer 38 over signal path 36. Signal path 36 may sometimes bereferred to herein as IF path 36.

Harmonic rejection mixer 38 may include local oscillator phasegeneration circuitry such as programmable delay line 42, may include anarray of mixers such as mixer array 46, may include adjustable loadcircuitry such as adjustable load 50, and may include control circuitrysuch as controller 54. While control circuitry 14 is shown separatelyfrom wireless circuitry 24 in the example of FIG. 1 for the sake ofclarity, wireless circuitry 24 may include processing circuitry thatforms a part of processing circuitry 18 and/or storage circuitry thatforms a part of storage circuitry 16 of control circuitry 14 (e.g.,portions of control circuitry 14 may be implemented on wirelesscircuitry 24). As an example, baseband processor 26, some or all ofcontroller 54, and/or other portions of transmitter 28 may form a partof control circuitry 14.

Controller 54 may be coupled to programmable delay line 42 over controlpath 60. Controller 54 may provide control signals to programmable delayline 42 over control path 60 that control the operation of programmabledelay line 42. Controller 54 may be coupled to mixer array 46 overcontrol path 58. Controller 54 may provide control signals to mixerarray 46 over control path 58 that control the operation of mixer array46. Controller 54 may be coupled to adjustable load 50 over control path56. Controller 54 may provide control signals to adjustable load 50 overcontrol path 56 that control the operation of adjustable load 50.Adjustable load 50 may include analog-to-digital converter circuitrythat provides digital signals to controller 54 over control path 56(e.g., for use in calibrating harmonic rejection mixer 38). Adjustableload 50 may be coupled to antenna(s) 30 over radio-frequencytransmission line path 52.

Harmonic rejection mixer 38 is a multi-phase mixer that performsupconversion on IF signals IFIN using multiple phases of the localoscillator. For example, programmable delay line 42 may receivewaveforms LOC from LO generator 40 over LO path 41. Programmable delayline 42 may produce N LO phases LOi based on waveforms LOC (e.g., afirst LO phase LO0, a second LO phase LO1, a third LO phase LO2, an NthLO phase LON, etc.). Programable delay line 42 may provide LO phases LOito mixer array 46 over phase paths 44.

Mixer array 46 may receive IF signals IFIN from IF upconverter 34 overIF path 36. Mixer array 46 may include multiple mixer circuits arrangedin an array pattern (e.g., as a Gilbert cell). Mixer array 46 mayproduce output signals RFOUT on output path 48 based at least on the LOphases LOi received over phase paths 44. For example, when transmitter28 is transmitting radio-frequency signals RF′, mixer array 46 mayupconvert IF signals IFIN using LO phases LOi to produce output signalsRFOUT at radio frequencies. Adjustable load 50 may amplify the outputsignals RFOUT on output path 48 and may output the output signals toother circuitry in transmitter 28 for transmission by antenna(s) 30.Power amplifier circuitry, digital-to-analog converter (DAC) circuitry,and/or other circuitry in transmitter 28 (not shown in FIG. 1 for thesake of clarity) may operate on output signals RFOUT (e.g., at radiofrequencies) to produce the radio-frequency signals RF′ that aretransmitted by antenna(s) 30.

In general, the LO phases LOi used by mixer array 46 need to be arrangedin a way such that the third-order harmonic of the local oscillator canbe canceled out. However, if care is not taken, phase accuracy can bedifficult to maintain over channel frequency, operating temperature, andprocess variations, particularly for transmission atcentimeter/millimeter wave frequencies. Closed loop solutions to theseissues such as delay lock loop (DLL) solutions can work to combatvariations but also exhibit excessive phase noise. In order to mitigatethese issues regardless of variations in channel frequency, operatingtemperature, and process, harmonic rejection mixer 38 may perform openloop self-calibration operations.

The self-calibration operations may update the settings of programmabledelay line 42 over time so that the optimal local oscillator phases LOiare provided to mixer array 46 as device operating conditions changeover time. Harmonic rejection mixer 38 may therefore be operable in twooperating modes: a normal transmit mode in which harmonic rejectionmixer 38 produces radio-frequency signals RF′ for transmission byantenna(s) 30 and a calibration mode in which harmonic rejection mixer38 self-calibrates the settings of programable delay line 42. Performingself-calibration in the calibration mode may ensure that, when harmonicrejection mixer 38 is placed back into the transmit mode,radio-frequency signals RF′ are transmitted without undesirable EVMdegradation or emission mask violation.

FIG. 2 is a circuit diagram of harmonic rejection mixer 38. In theexample of FIG. 2, harmonic rejection mixer 38 performs upconversionusing N phases of the local oscillator. N may be any desired integer(e.g., N may be equal to two, three, four, five, six, seven, eight, morethan eight, etc.). As shown in FIG. 2, harmonic rejection mixer 38 mayinclude controller 54, adjustable load 50, mixer array 46, andprogrammable delay line 42. Controller 54 may be coupled to adjustableload 50 over control path 56 and may be coupled to mixer array 46 overcontrol path 58. Controller 54 may provide control signals CTRL1 toadjustable load 50 via control path 56 and may provide control signalsCTRL2 to mixer array 46 via control path 58. Control signals CTRL1 may,for example, reconfigure switches in adjustable load 50 as harmonicrejection mixer 38 transitions between the transmit mode and thecalibration mode. Similarly, control signals CTRL2 may reconfigureswitches in mixer array 46 as harmonic rejection mixer 38 transitionsbetween the transmit mode and the calibration mode.

Controller 54 may be coupled to programmable delay line 42 over controlpath 60. Controller 54 may provide control signals CTRL3 to programmabledelay line 42 via control path 60. Control signals CTRL3 may, forexample, identify phase tuning settings such as a phase code forprogrammable delay line 42. Programmable delay line 42 may receive localoscillator waveforms LOC from LO generator 40 (FIG. 1) over LO path 41.Programmable delay line 42 may generate N LO phases LOi based onwaveforms LOC and may output LO phases LOi onto phase paths 44 (e.g.,programmable delay line 42 may output a first LO phase LO0 on a firstphase path 44-0, may output a second LO phase LO1 on second phase path44-1, may output a third LO phase LO2 on third phase path 44-2, mayoutput an Nth LO phase LON on Nth phase path 44-N, etc.).

Programmable delay line 42 may include N cascaded delay cells 62 (e.g.,a first delay cell 62-0, a second delay cell 62-1, a third delay cell62-2, an Nth delay cell 62-N, etc.). Each delay cell 62 may include afirst inverter 64 (e.g., a logic NOT gate), a second inverter 66 (e.g.,a logic NOT gate), and an adjustable capacitance 68. The output of firstinverter 64 may be coupled to the input of second inverter 66 and to theinput of the first inverter 64 of the next delay cell 62 of programmabledelay line 42. The output of second inverter 66 may be coupled to arespective phase path 44. The input of first inverter 64 may be coupledto the output of the first inverter 64 and the input of the secondinverter 66 of the previous delay cell 62 of programmable delay line 42.Adjustable capacitance 68 may be coupled between the output of firstinverter 64, the input of the second inverter 66, and control path 60.The output of the first inverter in Nth delay cell 62-N may be coupledto the input of the second inverter in Nth delay cell 62-N without beingcoupled to the input of any other delay cells 62 (e.g., becauseprogrammable delay line 42 includes only N delay cells 62). The input ofthe first inverter 64 in first delay cell 62-0 may be coupled to LO path41.

First delay cell 62 may output first LO phase LO0 on phase path 44-0based on the waveforms LOC received over LO path 41. The inverters ineach subsequent delay cell 62 may apply an equally spaced phase delay αto the LOC waveforms received from the output of the previous delay cell62 to produce the remaining (N-1) LO phases LOi on phase paths 44-1through 44-N (e.g., second LO phase LO1 may be at a phase that is −αwith respect to the phase of first LO phase LO0, third LO phase LO2 maybe at a phase that is −α with respect to the phase of second LO phaseLO1 and that is −2α with respect to the phase of first LO phase LO0,etc.).

Adjustable capacitances 68 may be formed from banks of discretecapacitors or varactors, as examples. The phase code identified bycontrol signal CTRL3 may control adjustable capacitances 68 to exhibit aselected capacitance. When harmonic rejection mixer 38 is operating inthe calibration mode, control circuitry 54 may sweep through differentphase codes in control signal CTRL3 to adjust the selected capacitanceof adjustable capacitances 68. This change in the selected capacitancemay serve to tweak the LO phases LOi produced by programmable delay line42 so optimal LO phases LOi can be provided to mixer array 46 even asoperating conditions change over time.

As shown in FIG. 2, mixer array 46 may include N mixer circuits 70(e.g., a first mixer circuit 70-0, a second mixer circuit 70-1, an Nthmixer circuit 70-N, etc.). Mixer circuits 70 may, if desired, bearranged in a Gilbert cell configuration. Each of the N mixer circuits70 may be coupled in parallel between IF path 36 and output path 48.Adjustable load 50 may also be coupled to output path 48. Mixer array 46may have an IF input port coupled to IF path 36, an output port coupledto output path 48, and N LO phase input ports coupled to phase paths 44.The gain coefficient of each mixer circuit 70 may be given by thesizing, biasing, and/or polarity swapping of the circuitry within themixer circuit, for example.

Each mixer circuit 70 in mixer array 46 may have a first input coupledto a respective input path 78 and a second input coupled to a respectivephase path 44 (e.g., mixer circuit 70-0 may have a first input coupledto input path 78-0 and a second input coupled to phase path 44-0, mixercircuit 70-1 may have a first input coupled to input path 78-1 and asecond input coupled to phase path 44-1, mixer circuit 70-N may have afirst input coupled to input path 78-N and a second input coupled tophase path 44-N, etc.). Each mixer circuit 70 may receive a respectiveLO phase LOi over the corresponding phase path 44 (e.g., mixer circuit70-0 may receive the LO phase LO0 produced by delay cell 62-0 over phasepath 44-0, mixer circuit 70-1 may receive the LO phase LO1 produced bydelay cell 62-1 over phase path 44-1, mixer circuit 70-N may receive theLO phase LON produced by delay cell 62-N over phase path 44-N, etc.).Each input path 78 may be coupled to IF path 36 through a respective IFswitch 76 (e.g., IF switch 76-0 may couple IF path 36 to input path78-0, IF switch 76-1 may couple IF path 36 to input path 78-1, IF switch76-N may couple IF path 36 to input path 78-N, etc.).

The input path 78 for each mixer circuit 70 may be coupled to the phasepath 44 of the next mixer circuit 70 in mixer array 46 over a respectiveinter-mixer path 72. A respective inter-mixer switch 74 may beinterposed on each inter-mixer path 72. For example, as shown in FIG. 2,input path 78-0 for mixer circuit 70-0 may be coupled to the phase path44-1 for mixer circuit 70-1 via inter-mixer path 72-0 and inter-mixerswitch 74-0, input path 78-1 for mixer circuit 70-1 may be coupled tothe phase path for the next mixer circuit in mixer array 46 viainter-mixer path 72-1 and inter-mixer switch 74-1, input path 78-N formixer circuit 70-N may be coupled to the phase path 44-0 for mixercircuit 70-0 via inter-mixer path 72-N and inter-mixer switch 74-N, etc.

Controller 54 may control the state of the switches 76 and 74 in mixerarray 46 (e.g., using control signals CTRL2) based on whether harmonicrejection mixer 38 is being operated in the transmit mode or thecalibration mode. In the transmit mode, controller 54 may openinter-mixer switches 74 while closing IF switches 76. Mixer circuits 70will thereby upconvert IF signals WIN to produce output signals RFOUT atradio-frequencies (e.g., using the LO phases LOi received fromprogrammable delay line 42). In the transmit mode, controller 54 mayalso control adjustable load 50 (e.g., using control signals CTRL1) toamplify output signals RFOUT for transmission to antenna(s) 30 (e.g., asradio-frequency signals RF′ of FIG. 1).

In the calibration mode, controller 54 may open IF switches 76 whileclosing inter-mixer switches 74. This may configure mixer array 46 toform a phase detector in which the LO phase from the next mixer circuit70 in mixer array 46 is provided to the first input of each mixercircuit 70. Each inter-mixer path 72 may have a path delay that producesa corresponding phase delay δ, which is output by mixer array 46 atoutput path 48 (e.g., output signals RFOUT may be a DC voltage thatidentifies phase delay δ in the calibration mode). Phase delay δ maysometimes be referred to herein as routing phase delay δ. Adjustableload 50 may generate digital output DO based on the DC voltage output bymixer array 46. Controller 54 may process digital output DO to calibratethe LO phase settings of programmable delay line 42 (e.g., to provideprogrammable delay line 42 with a phase code in control signals CTRL3that produces LO phases LOi that optimize performance by the transmitterfor the current operating conditions).

FIG. 3 is a state diagram illustrating how harmonic rejection mixer 38may toggle between a transmit mode 80 and a calibration mode 82. Whenharmonic rejection mixer 38 is operated in transmit mode 80 (sometimesreferred to herein as normal mode 80), harmonic rejection mixer 38upconverts IF signals IFIN to radio frequencies and transmitter 28transmits the corresponding radio-frequency signals RF′ to antenna(s)for transmission (FIG. 1).

In transmit mode 80, the inter-mixer switches 74 in mixer array 46 areopen. The IF switches 76 in mixer array 46 are closed. Programmabledelay line 42 generates LO phases LOi for mixer array 46. Mixer array 46generates output signals RFOUT at radio frequencies (on output path 48)by upconverting the IF signals IFIN on IF path 36 using LO phases LOi.Switches in adjustable load 50 may be closed in transmit mode 80.Adjustable load 50 amplifies output signals RFOUT and outputs theamplified signals onto radio-frequency transmission line path 52 fortransmission by antenna(s) 30.

Controller 54 may monitor for a trigger condition that would trigger atransition from transmit mode 80 to calibration mode 82. The triggercondition may occur when wireless performance metric data associatedwith transmitter 28 reaches a curtained predetermined threshold (e.g.,when gathered EVM data exceeds a threshold value, when spectralviolations occur, etc.), may occur after a predetermined amount of time,may occur when the frequency used to transmit radio-frequency signalsRF′ changes (e.g., when transmitter 28 changes the frequency channel fortransmission), may occur when temperature sensor data gathered bycontroller 54 indicates that device 10 has undergone a predeterminedchange in temperature, etc.

When harmonic rejection mixer 38 is operated in calibration mode 82(sometimes referred to herein as self-calibration mode 82), harmonicrejection mixer 38 forms a phase detector that provides digital outputDO to controller 54 based on local oscillator phases LOi. For example,in calibration mode 82, inter-mixer switches 74 may be closed. IFswitches 76 may be open. The switches in adjustable load 50 may be open.Mixer array 46 may form a phase detector that generates output signalsRFOUT as a DC voltage on output path 48. The DC voltage may identify therouting phase delay δ associated with inter-mixer paths 72 and/or thephase delay α produced by delay cells 62. Adjustable load 50 may providethe DC voltage to an analog-to-digital converter (ADC). The ADC maygenerate digital output DO based on the DC voltage (e.g., a digitalsignal that identifies routing phase delay δ and/or phase delay α).Controller 54 may receive digital output DO. Controller 54 may calibrateharmonic rejection mixer 38 based on the received digital output DO. Forexample, controller 54 may sweep through different phase codes providedto programmable delay line 42. Controller 54 may use the digital outputDO produced during each step of the sweep to identify a setting forprogrammable delay line 42 (e.g., a phase code) that optimizesperformance. The phase code may correspond to a zero crossing point ofthe DC voltage. Once the optimal setting for programmable delay line 42,controller 54 may place harmonic rejection mixer 38 back into transmitmode 80. Harmonic rejection mixer 38 may then produce output signalsRFOUT at radio frequencies for transmission (e.g., using LO phases LOiproduced by the optimal setting for programmable delay line 42 asidentified in calibration mode 82).

FIG. 4 is a circuit diagram of harmonic rejection mixer 38 whileoperated in transmit mode 80. In the example of FIG. 4, controller 54and programmable delay line 42 are not shown for the sake of clarity. Inthis example, there are N=3 mixer circuits 70 in mixer array 46 (e.g., afirst mixer circuit 70-0, a second mixer circuit 70-1, and a third mixercircuit 70-2). Similarly, there are N=3 LO phases LOi that are producedby programmable delay line 42 (e.g., programmable delay line 42 may havea first delay cell 62-0 that produces a first LO phase LO0, a seconddelay cell 62-1 that produces a second LO phase LO1, and a third delaycell 62-2 that produces a third LO phase LO2). This is merelyillustrative and, in general, N may be any desired integer.

In the example of FIG. 4, IF signals IFIN and output signals RFOUT aredifferential signals. Output signals RFOUT therefore includedifferential signal pair RFOUTP/RFOUTN. Output path 48 (FIG. 2) includesdifferential output lines 48P/48N (e.g., where differential output line48P conveys differential output signal RFOUTP and differential outputline 48N conveys differential output signal RFOUTN). Similarly, IFsignals IFIN include differential signal pair IFINP/IFINN. IF path 36(FIG. 2) includes differential IF lines 36P/36N (e.g., wheredifferential IF line 36P conveys differential IF signals IFINP anddifferential IF line 36N conveys differential IF signals IFINN). FIG. 4illustrates the operation of mixer array 46 only on differential IFsignals IFINP for the sake of clarity. Similar operations may also beperformed on differential IF signals IFINN. This example is merelyillustrative and, in another suitable arrangement, IF signals IFIN andoutput signals RFOUT may be single-ended signals.

As shown in FIG. 4, IF switches 76-0, 76-1, and 76-2 are closed intransmit mode 80. At the same time, inter-mixer switches 74-0, 74-1, and74-2 are open. Controller 54 may control the states of inter-mixerswitches 74 and IF switches 76 using control signals CTRL2 provided overcontrol path 58 (FIG. 2). Mixer circuit 70-0 may upconvert the IFsignals IFIN that pass through IF switch 76-0 using LO phase LO0. Mixercircuit 70-1 may upconvert the IF signals IFIN that pass through IFswitch 76-1 using LO phase LO1. Mixer circuit 70-2 may upconvert the IFsignals IFIN that pass through IF switch 76-2 using LO phase LO2. Mixercircuits 70-0, 70-1, and 70-3 may output corresponding output signalsRFOUT (e.g., differential signal pair RFOUTP/RFOUTN) on output path 48.Output signals RFOUT may be at radio frequencies (e.g., frequencieswithin the frequency band(s) of operation of antenna(s) 30 of FIG. 1).

In order to cancel out the third-order harmonic of the local oscillator,mixer circuit 70-1 may be twice the size of mixer circuit 70-0 and maybe twice the size of mixer circuit 70-2 (e.g., the three mixer circuitsin mixer array 46 may have a 1:2:1 size ratio). If, for example, LOphase LO0 has a phase of zero degrees, LO phase LO1 may have a phase of−α (e.g., as imparted by the first and second delay cells inprogrammable delay line 42) and LO phase LO2 may have a phase of −2α(e.g., as imparted by the first, second, and third delay cells inprogramable delay line 42). In this example, α may be 60, 120, or 240degrees. In scenarios where α=120 or 240, the output signals produced bymixer circuit 70-0 and mixer circuit 70-2 may be inverted (e.g., atoutputs 97 coupled to output path 48). If desired, this phase invertingmay be performed by swapping the RFOUTP and RFOUTN connections in themixer circuit (in examples where the mixer circuit is a differentialcircuit).

Adjustable load 50 may include transistor 94 (e.g., a PMOS transistor),transistor 98 (e.g., a PMOS transistor), a first inductor L1, a secondL2, a first resistor R1, a second resistor R2, a power supply terminal92, a first switch 90, a second switch 84, and a third switch 86. Thedrain terminal of transistor 94 may be coupled to differential outputline 48P. The source terminal of transistor 94 may be coupled to powersupply terminal 92. The gate terminal of transistor 94 may be coupled tocircuit node 88. The drain terminal of transistor 98 may be coupled todifferential output line 48N. The source terminal of transistor 98 maybe coupled to power supply terminal 92. The gate terminal of transistor98 may be coupled to circuit node 88. Switch 90 may be coupled betweencircuit node 88 and power supply terminal 92. Power supply terminal 92may receive a power supply voltage such as power supply voltage VDD.

Inductor L1 and switch 84 may be coupled in series between differentialoutput line 48P and circuit node 88. Resistor R1 may be coupled inparallel with switch 84 between inductor L1 and circuit node 88.Inductor L2 and switch 86 may be coupled in series between differentialoutput line 48N and circuit node 88. Resistor R2 may be coupled inparallel with switch 86 between inductor L2 and circuit node 88. An ADCsuch as comparator 100 may have a first input terminal coupled todifferential output line 48P and a second input terminal coupled todifferential output line 48N. Comparator 100 may have an output terminal102 that is coupled to controller 54 over control path 56 (FIG. 2).Comparator 100 may be unused during transmit mode 80.

In transmit mode 80, switches 84, 86, and 90 are closed. Controller 54may control the states of switches 84, 86, and 90 using control signalsCTRL1 provided over control path 56 (FIG. 2). Circuit node 88 (e.g., acenter tap of adjustable load 50) may be shorted to power supply voltageV_(DD) through switch 90. There may be no or negligible current passingbetween the source and drain terminals of transistors 98 and 94. Currentmay bypass resistors R1 and R2 through switches 84 and 86. This mayconfigure adjustable load 50 to form a differential inductor at theradio frequencies of output signals RFOUT (e.g., a differential inductorhaving an inductance given by inductors L1 and L2).

The differential inductor and a parasitic capacitance associated withmixer array 46 may form a resonant circuit. The resonant circuit mayresonate at the radio frequencies of output signals RFOUT and may serveto convert current from mixer array 46 into a corresponding voltage.This voltage may form across differential output lines 48P and 48N andmay be passed to additional circuitry in transmitter 28 for transmissionby antenna(s) 30. The resonant circuit may also serve to amplify thevoltage. Radio-frequency transmission line path 52 or other circuitry intransmitter 28 (FIG. 1) may be coupled to output terminals 104P and 104Non differential output lines 48P and 48N and may receive the amplifiedvoltage produced by adjustable load 50 over output terminals 104P and104N (e.g., for transmission as corresponding radio-frequency signalsRF′ of FIG. 4).

FIG. 5 is a circuit diagram of harmonic rejection mixer 38 whileoperated in calibration mode 82 of FIG. 3. As shown in FIG. 5, incalibration mode 82, IF switches 76-0, 76-1, and 76-2 may be open.Inter-mixer switches 74-0, 74-1, and 74-2 may be closed. Switches 90,84, and 86 in adjustable load 50 may be open. This may configure mixerarray 46 to form a phase detector and may configure adjustable load 50to form a DC amplifier.

For example, mixer circuit 70-0 may have a first input that receives LOphase LO1 from phase path 44-1 via inter-mixer path 72-0, inter-mixerswitch 74-0, and input path 78-0. Mixer circuit 70-0 may have a secondinput that receives LO phase LO0 over phase path 44-0. Similarly, mixercircuit 70-1 may have a first input that receives LO phase LO2 fromphase path 44-2 via inter-mixer path 72-1, inter-mixer switch 74-1, andinput path 78-1. Mixer circuit 70-1 may have a second input thatreceives LO phase LO1 over phase path 44-1. At the same time, mixercircuit 70-2 may have a first input that receives LO phase LO0 fromphase path 44-0 via inter-mixer path 72-2, inter-mixer switch 74-2, andinput path 78-2. Mixer circuit 70-2 may have a second input thatreceives LO phase LO2 over phase path 44-2.

Inter-mixer path 72-0 may impart a routing phase delay δ to LO phase LO1by the time LO phase LO1 is received at mixer circuit 70-0. Inter-mixerpath 72-1 may also impart routing phase delay δ to LO phase LO2 by thetime LO phase LO2 is received at mixer circuit 70-1. Likewise,inter-mixer path 72-2 may impart routing phase delay δ to LO phase LO0by the time LO phase LO0 is received at mixer circuit 70-2. In otherwords, routing phase delay δ may be the routing delay associated withthe inter-mixer paths 72 in mixer array 46. Mixer circuits 70 may mixeach of the LO phases together to produce a DC voltage V_(DC) acrossdifferential output lines 48P/48N (e.g., output signals RFOUT of FIG. 2may be DC voltage V_(DC) in calibration mode 82). DC voltage V_(DC) isdescribed mathematically by equation 1.

$\begin{matrix}{V_{DC} = {( {{\cos( {\alpha + \delta} )} - {2{\cos( {\alpha + \delta} )}} + {\cos( {{2\alpha} + \delta} )}} ) \times {GAIN}}} & (1)\end{matrix}$

In equation 1, GAIN is the gain imparted by adjustable load 50. Forexample, in calibration mode 82, inductors L1 and L2 and form a shortcircuit for the DC voltage and power supply voltage V_(DD) may bedecoupled from circuit node 88. This may configure adjustable load 50 toform a differential amplifier that applies gain GAIN to DC voltageV_(DC). The gain of the differential amplifier may be provided bytransistors 94 and 98 and resistors R1 and R2. The amplified DC voltageV_(DC) carries information identifying routing phase delay δ and phasedelay a (e.g., as given by equation 1) and may be passed to the firstand second inputs of an ADC such as comparator 100. Comparator 100 mayconvert DC voltage V_(DC) into digital output DO at output terminal 102(e.g., control path 56 of FIG. 2). Digital output DO may identifyrouting phase delay δ and/or phase delay α. The example of FIG. 5 inwhich a comparator produces digital output DO is merely illustrativeand, in general, comparator 100 may be replaced by any desired ADCcircuitry.

Controller 54 (FIG. 2) may process digital output DO to calibrateharmonic rejection mixer 38. For example, controller 54 may gatherdigital outputs DO as controller 54 sweeps through different phase codesthat are used by programmable delay line 42 to produce LO phases LOi.Controller 54 may process the gathered digital outputs DO to identify azero crossing point of DC voltage V_(DC) as a function of phase delay α.Assuming a routing phase delay δ of zero for now, the zero crossingpoint may be simplified from equation 1 and defined by equation 2 (theeffects of non-zero routing phase delays δ will be described shortly).

$\begin{matrix}{{{2\;{\cos^{2}(\alpha)}} - {\cos(\alpha)} - 1} = 0} & (2)\end{matrix}$

The zero crossing point may, for example, be found by solving equation 2for phase delay α. Three solutions (zero crossing points) for equation 2may be found: a first solution at 0 degrees, a second solution at 120degrees, and a third solution at 240 degrees. The second solution at 120degrees may exhibit asymmetry and poor linear range for differentrouting phase delays δ. At the same time, the third solution at 240degrees may exhibit larger linear range for a relatively large range ofrouting phase delays δ (e.g., equation 2 may resemble a line at the zerocrossing point at 240 degrees with a relatively constant slope for alarge range of routing phase delays such as routing phase delays δ from0 degrees to as high as 50 degrees or more). In general, either thesecond or third solutions (e.g., the second or third zero crossingpoints) may be used to perform harmonic rejection calibration (e.g., foridentifying an optimal phase code for the programmable delay line).

FIG. 6 is a circuit diagram of an illustrative mixer circuit 70 that mayto form any of the N mixer circuits in mixer array 46. As shown in FIG.6, mixer circuit 70 may include a first transistor 108, a secondtransistor 114, a third transistor 112, a fourth transistor 116, a fifthtransistor 110, and a sixth transistor 118. Transistors 108, 114, 112,116, 110, and 118 may be NMOS transistors, as an example. The sourceterminal of transistor 108 may be coupled to reference voltage 106(e.g., ground). The source terminal of transistor 110 may also becoupled to reference voltage 106.

The drain terminal of transistor 108 may be coupled to the sourceterminals of transistors 114 and 112. The drain terminal of transistor110 may be coupled to the source terminals of transistors 116 and 118.The drain terminals of transistors 114 and 116 may be coupled todifferential output line 48P. The drain terminals of transistors 112 and118 may be coupled to differential output line 48N. The gate terminal oftransistor 108 may receive differential IF signals IFINP. The gateterminal of transistor 110 may receive differential IF signals IFINN. Inthe differential signal example of FIG. 6, the LO phases LOi produced bythe programmable delay line may include a differential pair of LO phasesLOiP/LOiN. The gate terminals of transistors 114 and 118 may receivedifferential LO phases LOiP. The gate terminals of transistors 112 and116 may receive differential LO phases LOiN. Mixer circuit 70 may mixdifferential IF signal pair IFINP/IFINN using the differential pair ofLO phases LOiP/LOiN to produce differential output signal RFOUTP ondifferential output line 48P and to produce differential output signalRFOUTN on differential output line 48N. The example of FIG. 6 is merelyillustrative. Mixer circuit 70 may be implemented using otherarchitectures and/or may operate on single-ended signals if desired. Theconnections of differential output lines 48P and 48N as shown in FIG. 6may be swapped to invert the output of the mixer circuit if desired(e.g., for forming mixer circuits 70-0 and 70-3 of FIGS. 5 and 6).

FIG. 7 is a flow chart of illustrative steps that may be performed bycontroller 54 in calibrating harmonic rejection mixer 38 based ondigital output DO from adjustable load 50. The steps of FIG. 7 may, forexample, be performed by controller 54 while harmonic rejection mixer 38is in calibration mode 82 of FIG. 3 (e.g., while harmonic rejectionmixer 38 is configured as shown in the circuit diagram of FIG. 5).

At step 120, controller 54 may close inter-mixer switches 74 in mixerarray 46 (e.g., using control signals CTRL2 of FIG. 2).

At step 122, controller 54 may open IF switches 76 in mixer array 46(e.g., using control signals CTRL2 of FIG. 2). Controller 54 maysubsequently begin to control programmable delay line 42 to sweepthrough different LO phases LOi that are provided to mixer array 46. Forexample, controller 54 may begin to sweep through different phase codesfor programmable delay line 42.

At step 124, to begin sweeping through phase codes, controller 54 mayprovide an initial phase code to programmable delay line 42 (e.g., usingcontrol signals CTRL3 provided over control path 60 of FIG. 2). Theinitial phase code may configure adjustable capacitances 68 to exhibit acorresponding capacitance, thereby configuring each delay cell 62 inprogrammable delay line 42 to introduce a corresponding phase delay α inproducing LO phases LOi based on LO waveforms LOC.

Mixer array 46 may receive the LO phases LOi produced by programmabledelay line 42 using the initial phase code. Mixer array 46 may produce acorresponding DC voltage V_(DC) on output path 48. DC voltage V_(DC) mayidentify the routing phase delay δ produced by the inter-mixer paths 72in mixer array 46 and/or the phase delay α of the programmable delayline. Comparator 100 may produce digital output DO using DC voltageV_(DC). Digital output DO may, for example, be a digital version of DCvoltage V_(DC).

At step 126, controller 54 may identify and store digital output DO forfurther processing. The stored digital output DO may, for example,identify a corresponding routing phase delay δ and/or phase delay α(e.g., as given by equation 1).

If phase codes in the sweep remain for processing (e.g., phase codesfrom all of the possible phase codes for adjustable capacitances 68 ofFIG. 1), processing may proceed to step 130 as shown by arrow 128. Atstep 130, controller 54 may increment the current phase code (e.g.,controller 54 may identify the next phase code to use in the sweep ofphase codes).

At step 132, controller 54 may provide the current phase code (e.g., asidentified set during processing of step 130) to programmable delay line42. The current phase code may configure adjustable capacitances 68 toexhibit a different capacitance, thereby configuring each delay cell 62in programmable delay line 42 to introduce a different correspondingphase delay α in producing LO phases LOi based on LO waveforms LOC.Processing may then loop back to step 126, as shown by arrow 134.Controller 54 may then continue to gather and store the digital outputsDO produced by adjustable load 50 for each of the phase codes in thesweep.

When no phase codes remain in the sweep for processing, processing mayproceed to step 138 as shown by arrow 136. At step 138, controller 54may process the digital outputs DO stored during each iteration of step126 (e.g., the digital outputs DO produced using each phase code in thesweep of phase codes) to identify a zero-crossing point of the storeddigital outputs DO. As an example, the stored digital outputs DO mayinclude a sinusoidal curve that plots DC voltage V_(DC) (e.g., a digitalversion of the magnitude of DC voltage V_(DC)) as a function of phasedelay α. Controller 54 may have information that identifies which phasecode produced each phase delay α of the curve. This curve may have afirst zero crossing point at zero degrees, α second zero crossing pointat 180 degrees, and a third zero crossing point at 240 degrees, forexample. Controller 54 may identify the second or the third zerocrossing point as the zero crossing point to use for subsequentprocessing.

At step 140, controller 54 may provide the phase code that produced thephase delay α corresponding to the identified zero crossing point (e.g.,at 180 or 240 degrees) to programmable delay line 42. This phase codemay be used to set adjustable capacitances 68 to exhibit a selected(e.g., calibrated) capacitance. Programable delay line 42 may use theselected capacitance in producing calibrated LO phases LOi.

At step 142, controller 54 may place harmonic rejection mixer 38 backinto transmit mode 80 (FIG. 3). Harmonic rejection mixer 38 may produceoutput signals RFOUT at radio frequencies based on the calibrated LOphases LOi produced by programmable delay line 42 using the selectedcapacitance. Performing up-conversion using calibrated LO phases LOi mayallow harmonic rejection mixer 38 to mitigate odd-order harmonicinterference in the radio-frequency signals transmitted by antenna(s) 30given the present operating conditions at device 10. In this way,controller 54 may periodically or occasionally calibrate the operationof harmonic rejection mixer 38 so the harmonic rejection mixer canminimize EVM and spectral regrowth in the radio-frequency signals evenas device temperature, operating frequency, or other device conditionschange over time.

In general, different zero-crossing points maybe produced as thefrequency of the radio-frequency signals changes over time. FIG. 8 is aplot showing how different frequencies may produce differentzero-crossing points that are used for calibrating harmonic rejectionmixer 38. More particularly, FIG. 8 plots the DC voltage V_(DC) producedby mixer array 46 and adjustable load 50 (e.g., as identified by thedigital outputs DO stored by controller 54 at each iteration of step 126of FIG. 7) as a function of the phase code from the phase code sweepthat produced the DC voltage V_(DC). Phase code is plotted on thehorizontal axis as a phase code index, where each phase code indexcorresponds to a respective phase code from the sweep of phase codesperformed while processing the steps of FIG. 7 (e.g., a phase code of“25” represents the 25^(th) phase code from the sweep, a phase code of“50” represents the 50^(th) phase code from the sweep, etc.).

Curve 144 plots the DC voltage V_(DC) produced using a first frequencychannel, curve 146 plots the DC voltage V_(DC) produced using a secondfrequency channel, and curve 148 plots the DC voltage V_(DC) producedusing a third frequency channel. Curves 144, 146, and 148 are shown asonly having a single zero crossing point in FIG. 8 for the sake ofclarity (e.g., the 180 degree or 240 degree zero crossing point). Asshown by curves 144, 146, and 148, the particular frequency channel thatis used will change the zero crossing point of DC voltage V_(DC).

In scenarios where curve 144 is produced, controller 54 may identify thecorresponding zero crossing point 150 of DC voltage V_(DC) (e.g., thepoint where curve 150 crosses a voltage of zero). Controller 54 may usethe phase code corresponding to zero crossing point 150 to configure theadjustable capacitances 68 in programmable delay line 42. For example,as shown in FIG. 8, controller 54 may use the 25^(th) phase code fromthe sweep to configure the adjustable capacitances 68 in programmabledelay line 42. This may configure programmable delay line 42 to generatethe optimal LO phases LOi for mitigating harmonic interference whileoperating using the first frequency channel.

Similarly, in scenarios where curve 146 is produced, controller 54 mayidentify the corresponding zero crossing point 152 of DC voltage V_(DC)(e.g., the point where curve 146 crosses a voltage of zero). Controller54 may use the phase code corresponding to zero crossing point 152 toconfigure the adjustable capacitances 68 in programmable delay line 42.For example, as shown in FIG. 8, controller 54 may use the 50^(th) phasecode from the sweep to configure the adjustable capacitances 68 inprogrammable delay line 42. This may configure programmable delay line42 to generate the optimal LO phases LOi for mitigating harmonicinterference while operating using the second frequency channel.

Likewise, in scenarios where curve 148 is produced, controller 54 mayidentify the corresponding zero crossing point 154 of DC voltage V_(DC)(e.g., the point where curve 148 crosses a voltage of zero). Controller54 may use the phase code corresponding to zero crossing point 154 toconfigure the adjustable capacitances 68 in programmable delay line 42.For example, as shown in FIG. 8, controller 54 may use the 75^(th) phasecode from the sweep to configure the adjustable capacitances 68 inprogrammable delay line 42. This may configure programmable delay line42 to generate the optimal LO phases LOi for mitigating harmonicinterference while operating using the third frequency channel.

The example of FIG. 8 is merely illustrative. In practice, curves144-148 may have other shapes. While FIG. 8 illustrates how differentzero crossing points and thus different optimal phase codes may beidentified as operating frequency changes, the process of FIG. 7 may beused to identify the optimal phase code as device temperature changesover time, as frequency changes, and/or as any other operatingconditions change over time. This may serve to reduce the interferenceeffects of harmonics of the LO on the radio-frequency signals output bytransmitter 28 (e.g., radio-frequency signals RF′ of FIG. 1) by as muchas 10 dB or more, thereby optimizing the radio-frequency performance ofdevice 10. While the examples of FIGS. 1-8 describe harmonic rejectionmixer 38 as being formed in a wireless transmitter such as transmitter28, harmonic rejection mixer 38 may additionally or alternatively beformed in a wireless receiver (e.g., for performing harmonic rejectionoperations on signals received by antenna(s) 30).

Device 10 may gather and/or use personally identifiable information. Itis well understood that the use of personally identifiable informationshould follow privacy policies and practices that are generallyrecognized as meeting or exceeding industry or governmental requirementsfor maintaining the privacy of users. In particular, personallyidentifiable information data should be managed and handled so as tominimize risks of unintentional or unauthorized access or use, and thenature of authorized use should be clearly indicated to users.

The foregoing is merely illustrative and various modifications can bemade to the described embodiments. The foregoing embodiments may beimplemented individually or in any combination.

What is claimed is:
 1. A mixer array comprising: a first mixer circuitwith a first input configured to receive a first local oscillator (LO)phase, a second input coupled to an input path, and a first outputcoupled to an output path; a second mixer circuit with a third inputconfigured to receive a second LO phase, a fourth input coupled to theinput path, and a second output coupled to the output path; and a switchcoupled between the second input and the third input.
 2. The mixer arrayof claim 1 wherein the second LO phase is phase-delayed with respect tothe first LO phase.
 3. The mixer array of claim 1, wherein the mixerarray is configured to receive an input signal on the input path and isconfigured to produce an output signal on the output path, the outputsignal having a higher frequency than the input signal.
 4. The mixerarray of claim 3, wherein the output signal comprises a radio-frequencysignal.
 5. The mixer array of claim 1 further comprising: a third mixercircuit having a fifth input configured to receive a third LO phase, asixth input coupled to the input path, and a third output coupled to theoutput path; and an additional switch coupled between the fourth inputand the fifth input.
 6. The mixer array of claim 5, wherein the secondLO phase is phase-delayed with respect to the first LO phase and thethird LO phase is phase-delayed with respect to the first LO phase andthe second LO phase.
 7. The mixer array of claim 1, wherein the firstinput and the third input are coupled to a programmable delay line. 8.The mixer array of claim 7, wherein the first input is coupled to afirst delay cell in the programmable delay line and the second input iscoupled to a second delay cell in the programmable delay line.
 9. Themixer array of claim 1, further comprising: an additional switch thatcouples the input path to the second input.
 10. The mixer array of claim9, wherein the mixer array is configured to generate an output signal onthe output path while the additional switch is closed and while theswitch between the second input and the third input is open.
 11. Themixer array of claim 10, wherein the mixer array is configured togenerate a direct current (DC) voltage on the output path while theswitch between the second input and the third input is closed and whilethe additional switch is open.
 12. The mixer array of claim 1, whereinthe output path comprises first and second differential output lines.13. A method of operating mixer circuitry comprising: with a first mixercircuit, mixing a first LO phase with a second LO phase that isphase-delayed with respect to the first LO phase; with a second mixercircuit, mixing the second LO phase with a third LO phase that isphase-delayed with respect to the second LO phase; with at least thefirst and second mixer circuits, outputting a direct current (DC)voltage onto an output path; and with a controller, adjusting the first,second, and third LO phases based on the DC voltage on the output path.14. The method of claim 13, further comprising: with an adjustable loadcoupled to the output path, amplifying the DC voltage to generate anamplified DC voltage.
 15. The method of claim 14, further comprising:with an analog-to-digital converter (ADC) coupled to the output path,generating a digital output based on the amplified DC voltage.
 16. Themethod of claim 14, further comprising: with the controller, adjustingthe first, second, and third LO phases based on the digital output. 17.The method of claim 15, wherein adjusting the first LO phase produces afirst calibrated LO phase, adjusting the second LO phase produces asecond calibrated LO phase, and adjusting the third LO phase produces athird calibrated LO phase, the method further comprising: with the firstmixer circuit, mixing the first calibrated LO phase with an inputsignal; with the second mixer circuit, mixing the second calibrated LOphase with the input signal; with the first and second mixer circuits,generating radio-frequency signals on the output path based on the inputsignal, the first calibrated LO phase, and the second calibrated LOphase; amplifying the radio-frequency signals to produce amplifiedradio-frequency signals; and with an antenna, transmitting the amplifiedradio-frequency signals.
 18. Wireless circuitry comprising: an inputpath; an output path; a programmable delay line configured to generate aset of local oscillator (LO) phases; a mixer array coupled between theinput path and the output path, the mixer array being configured togenerate a radio-frequency signal on the output path based on an inputsignal on the input path and based on the set of LO phases; and anadjustable load coupled to the output path.
 19. The wireless circuitryof claim 18, wherein the adjustable load comprises: an inductor coupledto the output path; a first switch coupled in series between theinductor and a circuit node; a power supply terminal; a second switchcoupled between the power supply terminal and the circuit node; atransistor coupled between the output path and the power supplyterminal, the transistor having a gate terminal coupled to the circuitnode; and a resistor coupled between the inductor and the circuit nodein parallel with the first switch.
 20. The wireless circuitry of claim18, further comprising: a controller configured to operate the wirelesscircuitry in a transmit mode and in a calibration mode, wherein themixer array is configured to output the radio-frequency signal on theoutput path in the transmit mode and is configured to output adirect-current (DC) voltage on the output path in the calibration mode;and an analog-to-digital converter (ADC) coupled to the output path, theADC being configured to generate a digital output based on the DCvoltage in the calibration mode, and the controller being configured toadjust the set of LO phases produced by the programable delay line basedon the digital output in the calibration mode.